This invention relates to epoxy resin compositions. In one aspect, it relates to the curing of epoxy resin compositions. In a specific embodiment, the invention relates to increasing the pot life of epoxy resin compositions containing cationic curing agents.
Cationic curing agents for epoxy resins, such as Lewis acids (BF.sub.3 and SnCl.sub.4, for example) and their complexes, protonic acids containing anions of low nucleophilicity (HBF.sub.4, HPF.sub.6, HSbF.sub.6, CF.sub.3 SO.sub.3 H and H.sub.2 SO.sub.4, for example) and certain salts of these acids have a number of useful properties. Many of these curing agents will cure liquid epoxy resins to hard solids without the application of external heat within seconds or minutes after the resin and curing agent are mixed at room temperature. With some of the most active cationic curing agents, however, such as HBF.sub.4, cure may occur so rapidly (ten seconds or less) that complete mixing of the resin and curing agent is difficult. Dispensing of the resin-curing agent mixture is also difficult because of the very short pot life of the mixed system. Although cure can be retarded somewhat by lowering the ratio of curing agent to resin, this does not completely alleviate the problem. Cure can still occur so rapidly that droplets of curing agent are encapsulated by thin layers of cured resin, preventing diffusion of the curing agent throughout the resin.
It would therefore be desirable to decrease the cure rate of such a resin-curing agent mixture so that a homogeneous mixture could be formed and dispensed before curing occurred. Ideally, such a mixture would have a latent period before cure and a rapid rate of development of cured properties after the onset of cure.
It is therefore an object of the present invention to provide novel epoxy resin compositions. It is a further object to increase the pot life of epoxy resin systems containing cationic curing agents.